This invention relates to a process useful for the recovery of non-ferrous metal sulfide values from mineral ores by froth flotation.
Flotation is a process of treating a mixture of finely divided mineral solids, e.g., a pulverulent ore, suspended in a liquid whereby a portion of such solids is separated from other finely divided mineral solids, e.g., clays and other like materials present in the ore, by introducing a gas (or providing a gas in situ) in the liquid to produce a frothy mass containing certain of the solids on the top of the liquid, and leaving suspended (unfrothed) other solid components of the ore. Flotation is based on the principle that introducing a gas into a liquid containing solid particles of different materials suspended therein causes adherence of some gas to certain suspended solids and not to others and makes the particles having the gas thus adhere thereto lighter than the liquid. Accordingly, these particles rise to the top of the liquid to form a froth.
Various flotation agents have been admixed with the suspension to improve the frothing process. Such added agents are classed according to the function to be performed: collectors, for sulfide minerals including xanthates, thionocarbamates and the like; frothers which impart the property of forming a stable froth, e.g., natural oils such as pine oil and eucalyptus oil; modifiers such as activators to induce flotation in the presence of a collector, e.g., copper sulfate; depressants, e.g., sodium cyanide, which tend to prevent a collector from functioning as such on a mineral which it is desired to retain in the liquid, and thereby discourage a substance from being carried up and forming a part of the froth; pH regulators to produce optimum metallurgical results, e.g., lime, soda ash and the like.
It is of importance to bear in mind that additives of the hereinbefore described types are selected for use according to the nature of the ore, the mineral sought to be recovered, and the other additaments which are to be used in combination therewith.
An understanding of the phenomena which makes flotation a particularly valuable industrial operation is not essential to the practice of the present invention. They appear, however, to be largely associated with selective affinity of the surface of particulated solids, suspended in a liquid containing entrapped gas, for the liquid on the one hand, the gas on the other.
The flotation principle is applied in a number of mineral separation processes among which is the selective separation of such minerals as sulfide copper minerals, sulfide zinc minerals, sulfide molybdenum minerals and others from sulfide iron minerals.
Among collectors commonly used for the recovery of mineral values are xanthates, dithiophosphates, and thionocarbamates. When the ferrous-containing sulfide minerals are recovered in flotation processes along with the mineral values, there is excess sulfur present which is released in the smelting processes resulting in an undesirably high amount of sulfur present during the smelting operations. These volatile sulfur compounds are often released to the atmosphere through smokestacks, or are removed from such smokestacks by expensive and elaborate scrubbing equipment. Many nonferrous metal sulfides or metal oxides are found naturally in the presence of ferrous-containing sulfide ores.
Of the commercial collectors, the xanthates, thionocarbamates, and dithiophosphates do not selectively recover nonferrous metal values in the presence of ferrous sulfides. On the contrary, such collectors collect and recover all metal sulfides.
In many flotation processes the pH must be controlled to achieve the recovery of the desired minerals. Many of such processes give good recoveries under alkaline conditions and require the addition of large amounts of lime. This adds significant costs to such processes.
What is needed is a flotation process which will selectively recover the nonferrous metal sulfide values in the presence of ferrous sulfides. What is further needed is a collector which will selectively recover non-ferrous metal sulfides values under neutral and acidic conditions.
Furthermore, what are needed are collectors which give high rates of recovery of the metal sulfide values along with good selectivities towards the metal sulfide values over the gangue, that is, the undesired portions of the mineral ore.